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Friedel–Crafts Alkylation of Benzene and Dimethoxybenzene NAME: Mareh Altayar Howard Community College DATE: March 8th, 2021

Objective: 1. To illustrate the Friedel–Crafts alkylation of an activated benzene molecule with tertiary alcohol in the presence of sulfuric acid as the Lewis acid catalyst. 2. To synthesize

Chemical Index: 

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1,4 – Dimethoxybenzene ( C8H10O2 ) M.P: 57 – 58 ℃ M.W: 138.2 g/mol B.P: 212.6 ℃ Tert-Butyl Alcohol ( C4 H10 O ) M.P: 25 – 26 ℃ M.W: 74.1 g/mol B.P: 82°C 1-4-Di-t-Butyl-2,5 – dimethoxybenzene ( C16H26O2 ) M.P: 102 – 104 °C M.W: 250.4 g/mol B.P: 336.3ºC

Chemical RXN equation:

Procedures: 1. Dissolve 120 mg of 1,4-dimethoxybenzene in 0.4 mL of acetic acid and apply heat. 2. Add 0.2 mL of t-butyl alcohol and cool the mixture in an ice bath. 3. Use a Pasteur pipette to transfer the mixture within 0.4 ml of concentrated sulfuric acid and mix. 4. Warm it to room temperature for 10 minutes, then put it in ice. 5. Add 2.5 ml water to the mixture while stirring. 6. Remove the aqueous layer by a pipette, wash the crystals. Then leave them to dry for at least 24 hours.

Data & Calculations: Mass of funnel= 7.7331 1,4-dimethoxybenzene = 0.1307 g 1,4-Di-t-butyl-2,5-dimethoxybenzene (product mass) = 0.1602 g Mass of funnel + mass of product = 7.8933 g Melting point of 1,4-Di-t-butyl-2,5-dimethoxybenzene = 98.2 ℃ Theoretical yield: (Mass of 1,4-dimethoxybenzene / M.W of 1,4-dimethoxybenzene) X (M.W of 1,4-Di-t-butyl2,5-dimethoxybenzene) (0.1307 g / 138.2 g/mol) X (250.4 g/mol) = 0.2368 g/mol % yield: (Actual yield (product mass) / theoretical yield) X 100% (0.1602 g / 0.2368 g) X 100% = 67.65 %

Discussion: In this experiment, 1,4-dimethoxybenzene and t-butyl alcohol were reacted to form 1-tert-butyl-2,5-dimethoxybenzene. The reagent, 1,4-dimethoxybenzene, is highly reactive. This is because it is substituted with two methoxy electrondonating groups: activating groups and ortho-para directors. When 1,4dimethoxybenzene reacts with the t-butyl carbocation the first time, it adds ortho to one of the methoxy groups. A trisubstituted product called 1-tert-butyl-2,5dimethoxybenzene. This product contains two methoxy activating groups and one activating t-butyl group. This product is even more reactive than the initial, 1,4dimethoxybenzene product. Thus, this allows for another edition of the t-butyl

cation.3 This addition occurs in the ortho position to the other methoxy group. The final product formed is 1-tert-butyl-2,5-dimethoxybenzene. In this experiment, acetic acid was used as a solvent. Acetic acid makes a suitable solvent for this reaction because it can dissolve polar and non-polar compounds. It also can act as a nucleophile to trap carbocations. An ice bath was used in this reaction to aid in the process of recrystallization. Slow cooling of the solution allows for the formation of pure crystals. Initially, stirring the mixture with a glass rod also aided in the recrystallization process by scratching off small pieces of glass off the beaker. These small pieces of glass act as nuclei for crystal formation.5 The addition of cold water to the solution also helped with recrystallization. The percent yield calculated in this experiment was 67.65% which is considered good. Still, several errors could have occurred to give this percent yield. Multiple transfers of the mixture between glassware happened during this experiment. Anytime a mixture is transferred between glassware, there is a risk for the loss of product. Also, not all of the crystallized product was able to be removed. Another error that could have occurred was that not all of the product could have crystallized out of the mixture. The melting point obtained for the final product was a range from 98.2°C to 105.0°C. The melting point of pure 1-tert-butyl-2,5-dimethoxybenzene is a range from 102.0°C to 104.0°C.2 The melting point observed is slightly lower and broadened. This indicates the presence of impurities. Impurities could have been recrystallized from the rapid cooling of the mixture. Water or unreacted products could have also been present in the product mixture, which could have given this melting point range. In this experiment, 1,4-dimethoxybenzene and t-butyl alcohol were reacted to form 1-tert-butyl-2,5-dimethoxybenzene. The final product obtained was an excellent 1tert-butyl-2,5-dimethoxybenzene. This was confirmed by analysis of melting point and calculation of percent yield. More analysis could have been done on the final product to determine its purity. IR spectroscopy could have been done to confirm the functional groups on the final product. Proton NMR spectroscopy could have been done to determine the hydrogen structure of the final product

Work cited:

The PubChem Project https://pubchem.ncbi.nlm .nih.gov/ (accessed Apr 10, 2017) 3

Friedel-Crafts Alkylation of Dimethoxybenzene http://www.organicchem.or g/oc2web/lab/exp/fc/ fcdes.html (accessed Apr 10, 2017). 4

Sell, C. S. The chemistry of fragrances: from perfumer to consumer; RSC Publishing:

Cambridge, UK, 2006. 5

Wired Chemist http://www.wiredchemist.co m/chemistry/instructional/la boratory-tutorials/ recrystallization (accessed Apr 10, 2017). 6

Friedel-Crafts Alkylation of 1,4-Dimethoxybenzene http://web.mnstate.edu/jasp erse/Chem365/ Friedel-Crafts %20Alkylation.pdf (accessed Apr 10, 2017) The PubChem Project https://pubchem.ncbi.nlm.nih.gov/ (accessed March 8th, 2021)

Friedel-Crafts Alkylation of Dimethoxybenzene http://www.organicchem.org/oc2web/lab/exp/fc/fcdes.html (accessed March 8th, 2021). Sell, C. S. The chemistry of fragrances: from perfumer to consumer; RSC Publishing: Cambridge, UK, 2006. Wired Chemist http://www.wiredchemist.com/chemistry/instructional/laboratorytutorials/recrystallization (accessed March 8th, 2021). Friedel-Crafts Alkylation of 1,4-Dimethoxybenzene http://web.mnstate.edu/jasperse/Chem365/Friedel-Crafts%20Alkylation.pdf (accessed March 8th, 2021)...